Towards a consistent understanding of the exotic nucleus ⁴²₁₄Si₂₈

The issue of magicity of ⁴²₁₄Si₂₈ has been a contentious one. Friedmann et al., through studies of two-proton knockout reaction ⁴⁴₁₆Si₂₈ ⟶ ⁴²₁₄Si₂₈, presented strong evidence in support of magicity and sphericity of ⁴²₁₄Si₂₈. However in complete conflict with this, Bastin et al., gave equally strong empirical evidence, to show that the N = 28 magicity had completely collapsed in ⁴²₁₄Si₂₈ to make it well deformed. The consensus at present though is in favour of the validity of the latter experiment. However, our QCD based theoretical model supports the result of Friedmann experiment. They had explored the amazing persistence of the unique exotic nucleus ⁴²₁₄Si₂₈ as a stable structure within the nucleus ⁴⁸₂₀Ca₂₈; even after stripping off six-protons through the isotonic chain:⁴⁸₂₀Ca₂₈ ⟶ ⁴⁶₁₈Ar₂₈ ⟶⁴⁴₁₆ S₂₈ ⟶ ⁴²₁₄Si₂₈. Thus it is the novel and unexpected stability of proton shell closure at Z=14 in ⁴²₁₄, which is playing such a dominant role in ensuring its magicity, while the neutron magic number N = 28, goes into hiding or actually disappears. Recently, SAA has shown that the fusion experiment of a beam of halo nucleus ⁶He with the target nucleus ²³⁸U , actually provided strong evidence that the "core" of the halo nucleus has the structure of a tennis-ball (bubble) like nucleus, with a "hole" at the centre of its density distribution. This provides us with clear-cut support for our Quantum Chromodynamics based model of clusters of tritons in neutron-rich nuclei. Here we show that our QCD based model, provides support to Friedmann et al. , showing that, ⁴²₁₄Si₂₈ has a spherically magic structure of 14³₁H₂ (14-tritons) with a tennis-ball (bubble) like structure with "hidden" N=28 neutrons. (author)